This invention relates to automatic machines for edge trimming and beveling spectacle glasses, and more particularly relates to an improved automatic control device for lifting-up and translating operations in such a machine.
Machines for edge trimming and beveling spectacle glasses include a generally U-shaped carriage rotatably and slidingly mounted on a shaft extending through an intermediate part of said carriage, perpendicularly to the flanges thereof. A second rotating shaft comprised of two parts, each of which extends through one of said carriage flanges, is in parallel relationship with the first shaft and supports between its inner ends the spectacle glass to be treated. A jig is affixed to an end of one of the half-shafts.
A group of working grinding wheels is supported on a third shaft which is in parallel relationship with the first and second shafts and comprises a first flat rough grinding wheel and a finishing groove having a V-shaped cross-section.
A lifting-up and translation mecanism acts on the carriage so as to lower the glass to be trimmed against the rough grinding wheel, whereas the jig limits the lowering of the carriage by taking its bearing on a first rough-shaping stop, then that mechanism lifts up the glass with a pivoting motion about the first shaft, causes the carriage to translate to bring the glass above the finishing groove of the grinding wheel and finally lowers said glass to bring its edge into contact within said finishing groove of the grinding wheel, whereas the jig comes to rest on a second finishing stop when treatment of the glass is completed.
In machines of that kind heretofore known, the device which controls lifting-up and lowering of the glass onto the grinding wheels ensures said motions along a vertical path and also in any angular position of the glass.
Curvature changes of the glasses, which depend on the type of correction to be achieved, as well as diameter changes of these glasses however alter the lateral falling position of the glass edge entering the grinding wheel groove, which has serious diadvantages:
the lateral positions of the glass on the rough grinding wheel differ depending on its curvature and diameter, with the result that it is not easy to adjust the lateral position of the carriage above the rough grinding wheel and also causing an irregular wear of the grinding wheel throughout its width;
the edge of the glass does not fall always exactly in front of the groove of the wheel and during lifting-up the glass can be put in frictional engagement against one of the faces of the wheel groove, which results in marks or chamfers appearing on the bevel edges;
moreover when it is desired to make retouches on the glass on the finishing grinding wheel, said glass does not always present exactly the same face towards the finishing groove, which results in markings that only could be avoided through a manual adjusting or guiding operation so as to bring the glass edge directly opposite the finished groove.